1. EDS is a connective tissue disorder with skin and joint hypermobility.

[Table 2. Ehlers-Danlos Syndrome Classification]

2. Pathoanatomy

a. 40% to 50% of patients have a mutation in COL5A1 or COL5A2, the gene for type V collagen (type V collagen is important in the assembly of proper skin matrix collagen fibrils and of the basement membrane); this classic form is autosomal dominant.

b. Type VI, autosomal recessive, is a mutation in lysyl hydroxylase, an enzyme important in collagen cross-linking. Severe kyphoscoliosis is characteristic.

a. Nonsurgical—Most treatment is now medical, by rheumatologists, with a combination of NSAIDs and disease-modifying antirheumatic drugs (DMARDs). Most DMARDs are immunosuppressive and must be stopped before orthopaedic procedures and the cell count checked to avoid neutropenia.

b. Surgical—involves synovectomy and joint realignment early and joint arthroplasty in the later stages.

i. Reactive arthritis is triggered by an infectious disease such as Chlamydia, Yersinia, Salmonella, Campylobacter, or Shigella that causes an autoimmune complex deposition in the joints (commonly the knee), which leads to painful swelling.

ii. The mnemonic "Can't see, can't pee, can't climb a tree" is useful to remember the associated conjunctivitis and dysuria. Mouth ulcers and a rash on the hands and feet can occur.

iii. The underlying condition should be treated, and the arthritis should be managed supportively.

b. A history of breast-feeding with little sun exposure is the most likely scenario for vitamin D-deficient rickets.

4. Classification/treatment (

Table 4)

5. Surgery is indicated for lower limb bowing that does not resolve after medical treatment of the rickets; hemiepiphysiodesis or osteotomy may be indicated.

B. Trisomy 21 (Down syndrome)

1. Trisomy 21 is the most common chromosomal abnormality, with an incidence of 1 in 800 to 1,000 live births. Incidence increases with advanced maternal age.

2. Pathoanatomy—Usually a duplication of maternal

[Figure 4. Radiographic features of rickets. A, PA view of the wrist in a child with rickets shows radial and ulnar metaphyseal fraying and cupping (arrows). B, AP view of the lower extremities in a child with rickets demonstrates bowing of the femurs and tibias (white arrows) as well as metaphyseal widening and irregularity (black arrows).]

[Table 4. Most Common Types of Rickets With Associated Genetics, Features, and Treatment]

a. Supportive bracing is indicated for feet (supramalleolar or University of California at Berkeley Laboratory orthoses for pes planovalgus) and knees (patellar stabilizing braces) and for hips (hip abduction braces) in children younger than 6 years.

b. Atlanto-dens interval (ADI) of ≤5 mm is normal.

c. Treatment of asymptomatic ADI of 5 to 10 mm is controversial; many watch and obtain an MRI to look for cord compromise.

d. Fusion is indicated if cord compromise is seen on MRI or if there is ADI >5 and the patient has symptoms; however, fusion has a high (up to 50%) complication rate.